Proposed Dam Site Research Articles

Geomorphological and Sedimentological Rationale for Staged Sand Dam Construction

ABSTRACTStream sediment transport results from a convolution of climate, weather, geology, topography, biology, and human influence. In addition to providing water and food security for rural dryland communities, sand dams—small weirs designed to trap only the coarse fractions of transported sediments in seasonal and ephemeral streams—highlight many complexities of geomorphological dynamics. Sand dams store water in interstitial riverbed pores and the size of deposited sediment particles largely determines the recoverability of stored water: Fine materials limit transmission and provide lower volumetric yield. In this study, we seek to identify a practical method for evaluating the theoretical effect of staged sand dam crest construction on key sediment‐trapping processes for a proposed dam site. We argue that the Rouse number provides a useful criterion for identifying regimes where the target material grades are trapped. These ideas were tested using sediment data collected in Kenya and US Army Corps of Engineers River Analysis System numerical simulations to evaluate the sensitivity of sedimentation processes to crest height. We show that constructing sand dams in stages results in more targeted trapping of coarse material. Sedimentation is shown to be more sensitive to variation in crest height than the flood hydrograph, especially when a dam's crest height is small. By introducing a method to assess the necessity and inform design of staged crest construction based on local flow dynamics, this study offers a framework for optimising sand dam performance in data‐scarce environments. This approach provides a means to balance construction costs with expected benefits, enhancing the sustainability and functionality of sand dams in arid and semi‐arid regions.

A Proposed Dam Site Investigation Using Integrated Geophysical And Geotechnical Methods; A Case Study Of Loko Area, Northeastern Nigeria

A Proposed Dam Site Investigation Using Integrated Geophysical And Geotechnical Methods; A Case Study Of Loko Area, Northeastern Nigeria

Assessing foundation characteristics at the war dam site, lake tana basin, Ethiopia: A geophysical and geotechnical perspective

An integrated geophysical and geotechnical study evaluated the foundation conditions at the War dam site in northwest Ethiopia. This investigation included the classification of rock quality, shallow seismic refraction, and magnetic approaches. The dam's location comprises quaternary soil deposits and rhyolite rock units that have undergone varied weathering and fracturing. The shallow seismic refraction method distinguishes three layers of p-wave velocities that are less than 1.5 km per second with a depth range of 2–6 m, 1.5–2.5 km per second at a depth range of 15–20 m, and 2.5–3.5 km per second ranging from 20 to 40 m, respectively. Magnetic data were used to identify lineaments, and the RQD value acquired from boreholes ranged from extremely poor to excellent. Lineaments were recognized using the tilt angle approach. The results of the permeability tests demonstrated that the rock mass that serves as the dam's foundation had characteristics that are resistant to low permeability. The maximum and minimum lugeon values obtained from the testing were 9Lu and 0.81Lu, respectively. There are weak zones at and below the surface of the dam site, according to the overall findings acquired from seismic refraction, magnetic, and discontinuity surveying. These results were obtained from monitoring the dam site. These significant structures are directed towards a SW-NE, NE-SW, NNW-SSE, and SSW-NNE orientation. The study assessed the geological suitability of a proposed dam site using seismic refraction and magnetic survey methods. Significant geological variations were observed, particularly in the right abutment and valley floor, indicating the need for targeted grouting. The findings suggest that while the site is generally suitable for dam construction, specific areas require further ground improvement to ensure stability.

Evaluation of Carbonate and Heterogenous Rock Masses for the Dam Foundation: A Case Study at Kanarwe River Basin, Sulaimaniyah, NE Iraq

Evaluating rock masses for dam foundations, especially heterogeneous rock (flysch), becomes imperative and requires accurate geomechanical classifications. The rocks at the Kanarwe river basin, especially at a proposed dam site (Goma-Qazan near Khewata, Sura Qalat villages), mainly consist of interlaying massive carbonate rocks of the Aqra Formation with flysch rocks of Tanjero Formation. Therefore, selecting appropriate dam types is challenging and very risky. This study conducted a detailed study of lithology, discontinuity condition, rock sampling and laboratory tests to determine the site suitable for dam construction using the quantitative GSI, Rock Mass Rating, and Dam Mass Rating geomechanical classification systems. A new procedure was suggested for calculating stress relaxation and damage level (disturbance factor D) in rock masses. The Dam mass rating related to the foundation stability shows a good stability indication ranging from 43.7–82.9, indicating foundation suitability for all dam types. The foundation excavation desirability and consolidation grouting were evaluated based on dry basic rock mass rating, which shows that the site is suitable for earth fill and hardfill dams. However, the rock mass units require spot and systematic grouting for gravity and Arch dams, respectively. Ec/Em (deformation modulus of the dam/deformation modulus of foundation rocks) values for massive carbonate rock range from 0.18–0.93; they indicate site suitability for arch, gravity dam, earth fill and hardfill dams. While the Ec/Em values for flysch rock mass units range from 1–6.4, they indicate some units have a serious problem situation and need treatment based on the types of dams.

Debris Flow Run-Out Prediction Based on the Shallow-Water Flow Numerical Model—A Case Study of Xulong Gully

Here we present a method for predicting debris flow run-out based on a numerical model for shallow water flows, using a case study conducted on Xulong Gully, a proposed dam site for a hydropower station in the upper reaches of the Jinsha River. A field investigation and remote sensing interpretation methods were used to develop a comprehensive evaluation of debris flow zones and calculate the potential provenance volume in the Xulong Gully. Particle-size analysis was conducted on the early debris flow fan in the Xulong Gully to determine the rheological properties of the debris flow materials. A numerical model for shallow flows was constructed using the finite volume method to verify fluid motion across complex terrain and explore the debris flow run-out range with various provenance volumes. The model showed that for a total debris flow volume of less than two million m3, the debris flow impact area would remain within the Xulong Gully. However, if the total debris flow volume is more than two million m3, the debris flow would flush out into the Jinsha River, blocking a portion of the river. If all the provenance in the Xulong Gully were flushed out, the maximum flow velocity of the generated debris flow would be 11 m/s and the thickness of the debris flow at the Xulong Gully estuary would be about 28.8 m. The debris flow would completely block 470 m of the Jinsha River.

Suitable dam site identification using GIS-based MCDA: a case study of Chemoga watershed, Ethiopia

Ethiopia is Africa's second-most populous country, after Nigeria, and is primarily a farming community with low productivity that is heavily reliant on rain-fed agriculture. Water scarcity, global warming, and rising population all necessitate more effective water conservation methods. As a result, the demand for dams is increasing dramatically in order to provide the community with safe drinking water, electricity, and irrigation to ensure food security. The goal of this study was to use remote sensing and geographic information system (GIS) techniques in conjunction with the dam suitability stream model and multi-criteria decision analysis to identify potential sites for multi-purpose dam construction. The study used six influencing factors to find suitable dam sites, with the model's suitability stream and overall suitability output maps proposed and evaluated as a result. Based on the topography and land use, the results showed that three proposed dam sites in the upper part of the watershed are likely preferable for irrigation, fishery, and clean drinking water supply. The three proposed dam sites in the watershed's lower reaches, however, are better suited to hydropower generation. In addition, remote sensing and GIS are useful in dam/reservoir site selection because they allow decision-makers to create, manipulate, and manage relevant thematic layers.

Comparative study on dam site selection in the pre-feasibility stage of Shitouzhai Hydropower Station

The selection of dam site is the key content in the early stage of hydropower station project. Based on the hydrology, topographic and geological conditions, kinetic energy economic indexes, flood loss of reservoir, project layout, electromechanical and metal structure, construction conditions and project investment of the proposed dam site, this paper makes an in-depth analysis of the dam site selection in the pre-feasibility stage of Shitouzhai Hydropower Station, in order to provide beneficial inspiration for the design of similar projects.

Integrated Geophysical and Packer Test for the Water Tightness Evaluation of Gullele Botanic Garden Dam Site, Northwest of Addis Ababa, Ethiopia

Gullele Botanic Garden is one of the largest botanical gardens in Ethiopia, which is found northwest of Addis Ababa. For this garden, a dam was proposed to be constructed for irrigation and recreational purposes. The intended dam will have a height of 30 m and a dam axis length of around 180 m. The main objective of this work is to investigate and evaluate the engineering geological aspects of the proposed dam site based on detailed geological, geotechnical and geophysical investigations. The investigation conducted in the area includes, electrical resistivity imaging, VES, borehole drilling and single packer permeability test. Geologically the area is covered by the different volcanic rock such as ignimbrite, rhyolite, tuff, basalt, and residual soil; and geological structures such as joint, fracture, flow banding, and cooling joint. The dominant orientations of geological structures are N-S and E-W directions. Results from different investigations revealed that three geotechnical layers were identified. These are overburden (completely weathered ignimbrite and soil), highly to moderately weathered ignimbrite and moderately to slightly weathered ignimbrite rock mass. The rock mass permeability test from six boreholes has Lugeon values ranging from 0 to 9. The maximum Lugeon (permeability of the rock mass) values investigated at the left abutment and riverbed of the proposed dam site showed wash out and dilation behavior respectively. The permeability result indicates that possible seepage problem at left abutment, riverbed and reserviour of the proposed dam. Therefore, during the construction of the dam, those specific locations, which are identified as problematic areas, need effective ground improvement works and special monitoring.

Application of Vertical Electrical Sounding for Study the Proposed dam site at Wadi Ma’doo, Shabwah Governorate, Yemen

Application of geophysical investigation has been carried out using Vertical Electrical Sounding (VES) at the proposed site in wadi Ma’doo, Shabwah Governorate, Yemen to determine the geophysical parameters that can be used to evaluate the subsurface geological layering characteristics of the selection proposed site for dam construction. The Schlumberger array was used for the data acquisition. One-dimensional numerical inversion of individual DC resistivity was used to enhance the processing of the results for better achievement of the aim of the study. Model obtained from the 2D inversion of each VES were used for construction of geoelectric section which exhibit the main geoelectric characteristics of the geological units present in the site. The interpretation of the field data was carried out using the IP12WIN software, which converts the apparent resistivity as a function of electrode spacing to the true resistivity as a function of depth in two dimensions. The interpretation results showed that the geoelectric section consists of three layers namely: boulders and gravels, sandy to pebbly and hard limestone. The layer resistivities and thicknesses range from 18.17 to 746.20 Ω.m/0.20 to 1.084 m, 53 to 60 Ω.m/ 0.20 to 3.059 m and 455 to 1890 Ω.m, respectively. The investigation revealed that the limestone rocks is suitable for shallow foundation for proposed dam engineering structures.

Geological and Geoelectrical Investigation of a Proposed Dam Site Using Vertical Electrical Sounding at Osuworowo Stream, Utughughu Arochukwu, South Eastern Nigeria

Geophysical studies was carried out at a proposed dam site across Osuworowo stream in Arochukwu, south eastern Nigeria to investigate the depth to bedrock, possible geologic structures and foundation conditions of the dam axis. The study area is located between latitudes 5°23.58”N and 5°23.707”N and longitude 7°53.93”E and 7°53.97”E. Its elevation ranges from 90 ft to 149 ft. Six Vertical Electrical Soundings (VES) were carried out along the stream course using ABEM SAS 1000 TERRAMETER and this was done using Schlumberger configuration with maximum half current electrode separation of 55m able to reveal deep seated structures. The ip2win software was used to model the VES data to give resistivities which vary between 258 Ωm and 39000 Ωm with three and four geoelectric layer combinations of sand, sandstone, sandyshale, shalysand and ale units. The high resistivities of the geoelectric layers sand thickness and dip showing high gradient in elevation differences are indications that the site is suitable for the dam construction. The geological result shows the presence of faults this is confirmed by change in strike and dip.

Management of Treated Wastewater and Flood Water Using GIS for Environmental Protection in Jordan

Management of various water resources has become a pivotal need for all catchments and sub-catchements in Jordan. Storing treated wastewater applied in reservoirs that originally constructed to store flood and base flow water in the country. This practice has proved detrimental to the originally good quality reservoir waters, leading to additional water quality deterioration such as eutrophication issue. Hence, separating treated wastewater from flood and base flow waters to guarantee the availability of better quality waters for higher quality uses such as drinking or recreation. This study focuses on the dams constructed in Kafrain and Shueib catchments, lying west and northwest of Amman. The results of hydrological, hydrogeological, geological, water quality and terrain measurements using Remote Sensing, Geographical Information System (GIS) and Digital Elevation Models (DEM) show that there are nine potential dam sites in the two catchments to construct. In Shueib catchment, two proposed dam sites were selected as suitable dams for fresh water harvesting and groundwater artificial recharge. While, two suggested dam sites are located downstream of Al-Salt and Fuhais wastewater treatment plants for treated wastewater collection. In Kafrain catchment, three proposed dam sites were selected as suitable dams for fresh water harvesting and groundwater artificial recharge. Whereas, two suggested dam sites are located downstream of Wadi Sir wastewater treatment plant, hereby, it can be used to collect the treated wastewater. The study is expected to serve as an example for other catchments in Jordan and elsewhere, especially in water scarcity areas where treated waste water is stored together with flood and base flow waters.

Evaluating the distribution of freshwater fish diversity using a multispecies habitat suitability model to assess impacts of proposed dam development in Gabon, Africa

AbstractData scarcity impedes a comprehensive impact assessment of the 38 dams currently proposed within the highly biodiverse central African nation of Gabon. Here, we present a multiple‐species MaxEnt distribution modeling approach to assess species richness for freshwater fishes at the landscape level and demonstrate its utility in identifying proposed dam sites in Gabon that fall in highly diverse areas. We modeled habitat suitability for 202 of Gabon's fresh and brackish water fish species based on georeferenced presence data from museum specimens and a set of ecologically meaningful environmental conditions. We removed poor performing species from the model and compiled the distributions of 114 well‐performing species to generate a new metric, the species pseudorichness index (pR), defined as the cumulative number of species that are highly suited to the habitat in a given segment of river. We used pR as a proxy for true species richness and use this metric to evaluate the distribution of freshwater fish diversity relative to the proposed dam development in Gabon. We found that more than 80% of the proposed dams in Gabon overlap with areas of high pR, implying that planned hydroelectric development in Gabon may disproportionately affect high diversity areas. These dams deserve more focused baseline assessments and conservation action. This approach provides a rapid way to initiate a landscape‐scale assessment of freshwater fish diversity to inform conservation decisions in areas that are species rich, but data poor.

Planning for Environmental Water Allocations: Hydrology - Based Assessment in the Awash River Basin, Ethiopia

The research is financed by the Egyptian Government through the Nile Sector bilateral cooperation project Abstract With expanding water demand due to rapid socio-economic growth and shrinking supplies due to pollution and climate change impact, there is an increasing strain on the water resources of the Awash river basin. Furthermore, flow alterations due to the existing and the ongoing water resources infrastructure projects may adversely impact the natural life cycle of aquatic ecosystems in the river basin. In order to manage these consequences, compensation releases or allocation of environmental flows may be mandatory and calls for the establishment of environmental flows framework in Ethiopia. In this study, the environmental flows at selected five existing and proposed dam sites in the Awash river basin were investigated using six worldwide used hydrology-based methods, viz.: Desktop Reserve Model (DRM), Global Environmental Flow Calculator (GEFC), Tennant, Tessman, 7Q 10 and Q 95 . The environmental flow volumes from the six methods were compared on mean annual, monthly average and monthly basis and it is found that the predictions from the DRM and GEFC are more reliable than the others. Comparative results indicate that minimum annual average flow rates of 4.4 m 3 /s (15 % of Mean Annual Flow (MAF)), 10.5 m 3 /s (19 % of MAF), 16.4 m 3 /s (22 % of MAF), 2.5 m 3 /s (17 % of MAF) and 24.2 m 3 /s (26 % of MAF) are required at the immediate downstream reaches of Melka kuntre, Koka, Awash Compensation, Kesem and Tendaho dams respectively. Accordingly, the annual average environmental flow throughout the basin varies from 15-26 % of the natural MAF. Although preliminary, being the first attempt in the Awash river basin, this study is expected to stimulate dialogue among experts and decision makers in Ethiopia. Keywords: EFR, EFA, Tennant, Tessman, Q 95 , 7Q 10 , DRM, GEFC Software, Awash DOI : 10.7176/JEES/9-11-08 Publication date: November 30 th 2019

Dam site suitability assessment at the Greater Zab River in northern Iraq using remote sensing data and GIS

In the last few decades, the northern region of Iraq has been severely impacted by climate change, which has created long-term drought, water shortage, and casual flood events. Dam construction in suitable sites is a primary water management strategy to solve flood and drought. Dam site selection depends on a set of qualitative and quantitative criteria, such as geology, soil type, and altitude. In this study, appropriate areas of dam site selection for water management were identified using remote sensing, geographic information system (GIS), and multi-criteria decision making techniques. In addition, the proposed method of site suitability was evaluated by comparing it with the traditional analytic hierarchy process (AHP). A new validation method to evaluate the accuracy of AHP and fuzzy logic according to the preselected location of a dam was previously suggested in the study area (Bekhme dam) by the local government. Remote sensing data (Landsat imageries and ASTER DEM) and field/reference maps were used to derive 12 conditioning factors needed to produce a suitability map for construction. The criteria considered were geological formation, soil type, fault line, tectonic line, altitude, slope, rainfall data (2000–2011), water discharge, land use/cover, road network, and material used for dam construction. Two mathematical models, namely, AHP and fuzzy logic, were applied in this study. The best model was selected by using location and cluster-based accuracy assessment depending on the proposed dam site (i.e., Bekhme dam). Results showed that fuzzy logic is more accurate than AHP. In terms of the surface area of suitable lands identified, the AHP model determined 13,446,900 m2 as a highly suitable area, whereas the fuzzy model identified 3,409,200 m2 from the total area of 69,347,700 m2. Finally, this study identified four sites for intermediate and large dams in the study area. The total water capacities of proposed Dam 1, Dam 2, Dam 3, and Dam 4 are about 81.5, 239.3, 374.6, and 646.5 million m3, respectively, when the dam height is 60 m. The proposed methods can be easily replicated to other areas for similar applications. The finding reveals that AHP model is distributed and scattered in the whole study area, whereas the fuzzy model is more suitable for clustered areas.

ENGINEERING SITE INVESTIGATION USING 2D ELELCTRICAL RESISTIVITY TOMOGRAPHY AT THE SIKTAN PROPOSED DAM SITE AT ERBIL GOVERNORATE, IRAQI KURDISTAN REGION

2D Electrical Resistivity Tomography (ERT) was carried out at the proposed Siktan Dam site, Erbil Governorate, NE Iraq. The aim of this study is to evaluating the geo-structural setting of the concealed bedrock along the proposed dam axis and the flanks of the proposed dam site. A comprehensive geotechnical investigation consisting of borehole drilling works and electrical resistivity data were carried out to investigate the subsurface formation. Geologically the proposed dam site is located on the Shiranish Formation consisting of dark gray claystone alternating with limestone marlstone and sandstone. Three profiles were taken by Wenner array with 48 electrodes along of each profile which equal 235m, the space between electrodes is 5m. The SYSCAL PRO instrument is used to collect resistivity data and (SYSCAL Switch) were used with 48 electrodes along one line, and which carries out an automatic switching of these electrodes for acquiring profiling data. The data were processed and interpreted by applying 2D inversions TomoLab software. The using of geophysical prospecting in geotechnical investigation is sometimes looked at as a probable rather than certain method when it comes to construct a detailed subsurface layer profiles. The correlation between borehole information and electrical resistivity ranges was done. The combination of geophysical and geotechnical data may greatly improve the quality of buildings construction in civil engineering. From the structural point of view there is no faults have been detected in this location from ERT and boreholes data as well as there is no evidence of the existence of cavities or any other risky resources. The results indicate that the proposed site is suitable for construction of the dam. Boreholes and geotechnical investigations successfully used to verify the results of the resistivity measurements results.

Soil properties influencing erodibility of soils in the Ntabelanga area, Eastern Cape Province, South Africa

ABSTRACTSoil erosion has serious off-site impacts caused by increased mobilization of sediment and delivery to water bodies causing siltation and pollution. To evaluate factors influencing soil erodibility at a proposed dam site, 21 soil samples collected were characterized. The soils were analyzed for soil organic carbon (SOC), exchangeable bases, exchangeable acidity, pH, electrical conductivities, mean weight diameter and soil particles’ size distribution. Cation exchange capacity, exchangeable sodium percentage, sodium adsorption ratio, dispersion ratio (DR), clay flocculation index (CFI), clay dispersion ratio (CDR) and Ca:Mg ratio were then calculated. Soil erodibility (K-factor) estimates were determined using SOC content and surface soil properties. Soil loss rates by splashing were determined under rainfall simulations at 360 mmh−1 rainfall intensity. Soil loss was correlated to the measured chemical and physical soil properties. There were variations in soil form properties and erodibility indices showing influence on soil loss. The average soil erodibility and SOC values were 0.0734 t MJ−1 mm−1 and 0.81%, respectively. SOC decreased with depth and soil loss increased with a decrease in SOC content. SOC significantly influenced soil loss, CDR, CFI and DR (P < .05). The soil loss rate was 5.60 t/ha per 8 minute rainstorm of 360 mmh−1. Addition of organic matter stabilize the soils against erosion.

Land Capability Classification for Agro-economic Evaluation of Mahadayi Dam, Karnataka, India

This paper examines the socio-economic impact of proposed dam on cropland productivity of Mahadayi project, Karnataka, India. Systematic appraisal of dam and their designing by categories of classes on the basis of physical and chemical characteristics of soil has been done in favour of development of agronomic conditions for the study of proposed dam sites in Karnataka. The study is aimed at the effective utilization of land according to their classes. Documentation on the land capability classification is a versatile component in formulation effective land use planning before the construction of dam. Thus an attempt was made to evaluate dominantly occurring soils on four class’s viz. soil depth, soil texture, soil drainage and soil erosion. The study was focused on the evaluation of economics of crop production based on agro climatic condition of the study area and existing cropping pattern. This study is important as it explores how an input of water and nutrient would respond under variable climatic conditions. In addition, interactions of water supplies with fertilizer rates at optimizing these resources need have been investigated. This paper identifies key challenges and solutions for carrying out project-level economic analysis of adaptation to climate change, both stand-alone and integrated into broader development projects. Very few projects addressing adaptation thus far have been subject to in-depth and rigorous economic analysis for a variety of reasons, including a lack of guidance on how to deal with assessments of the impacts of climate change, as well as with estimating costs and benefits of adaptation under uncertainty. Our focus is on the agricultural sector, where the impacts of climate change have the potential to disrupt the livelihoods of rural populations in many regions and where adaptation must be given urgent consideration. Nevertheless, some of the approaches discussed are suitable to projects in other sectors. Key wordsSocio-Economic; Dam; Agronomic Condition; Land Capability Classification; Catchment Area; Crop Productivity; Land Suitability Maps

Electrical resistivity tomography, VES and magnetic surveys for dam site characterization, Wukro, Northern Ethiopia

Geophysical surveys involving the techniques of electrical resistivity imaging, electrical sounding and magnetics were employed to characterize the ground conditions at a proposed dam site at Hizaeti-Afras, Wukro, North Ethiopia. The techniques were utilized to map the depth to the competent formations, their relative suitability for foundation work and the presence and extent of weak zones in the subsurface. The work has mapped the different lithologic units of the subsurface and determined the depth to the basement rocks in the area. Through correlation of the inverse model resistivity sections of the imaging surveys, the geoelectric section of the sounding survey and the magnetic profile plots with available borehole lithologic logs, it is shown that the results very well supplement the geotechnical point data in addition to providing a wider coverage in mapping areas of weak ground that could otherwise be missed with widely spaced borehole information. The combined results of the survey show the proposed dam axis to be unsuitable. The power of the electrical resistivity imaging technique and its potential to map the shallow subsurface with adequate resolution are illustrated. The result is a strong suggestion that geophysical techniques can be used to assist and extrapolate borehole geotechnical data especially when large area is to be used for development of large infrastructure.

Study of Water &amp; Air Environment for Impact Analysis of Proposed Bhaurant Dam using Interaction Matrices Approach

This study presents the findings of Environmental Impact Assessment (EIA) for the proposedBhaurat Dam Project. In this study data pertaining to water and air environment within the study area 10 kms of radius from the dam site has been investigated in the upstream and downstream side of the proposed dam site. On the basis of impact analysis adopting using Matrice and Interaction Matrix approaches and results of the base-line data, it has been found that dam construction activity is more dominant over other aspects. Considered for correlation these aspects are effect on Regional Ecology and Environment, Irrigation Benefits, Forest Loss, Regional Economy, Social Aspects, Geology, Hydrology, Moreover, results indicate that there would be minimal adverse impact on regional ecology and environment following the construction of dam. Instead, it may offer benefit to this region. It may enhance irrigation activity leading to agricultural productivity, increase vegetation and green areas in this semi-arid region of the state.

Geoelectrical Investigation of a Proposed Dam Site in a Sedimentary Terrain: Case Study of Aba River at Amapu-Ideobia, Akanu Ngwa Southeastern Nigeria

The geoelectrical investigation of the proposed Aba River dam at Amapu-Ideobia, Akanu Ngwa Southeastern Nigeria has been carried out. The objective of this study is to determine the downward and lateral trends of the rock layers or units along and near the proposed dam axis and deduce the possible structures that may enhance workable design of the dam. ABEM Terrameter SAS 4000 model was used and the symmetrical Schlumberger configuration was adopted. Twelve (12) Vertical Electrical Sounding stations were located and fully occupied along the dam axis. Preliminary input data from the field were fed into Zohdy software to generate real resistivities and depths to geoelectric layers. Five geoelectric layers were interpreted as Loamy Top soil, Alluvial matter, Pebble bed, Sandy lateritic and Gravely sand. Layer 1 (the top loamy soil) was encountered in VES 1, 2, 3, 4, 5, 9, 10, 11 and 12 locations with maximum thickness of 1.5 m in VES 3 and 4. Resistivity values ranged from 216 to 519 Ohm-m. The second layer (lateritic matter) had a maximum lower depth of 5 m in VES 3 and 4 points. This was not encountered in VES 6 point being replaced by alluvium. Resistivity values ranged from 101 to 6190 Ohm-m. Layer 3 was interpreted as a restricted pebble bed which occurred only at VES 6, 7 and 8 locations flanking the river course with thickness of about 3.5 m and resistivity values range of 182 415 Ohm-m. The fourth layer was modeled as the alluvial matter and restricted to the river course (VES 6, 7, 8) locations with base at between 12.5 m in VES 8 and 8 m in VES 6. The last modeled layer (Layer 5) was composed of gravely sandstone that underlined the whole study area apart from the restricted pebble bed at the NE crestal portion (VES 12). No structures like fractures, lineaments and faults that would be of deleterious effect were observed in all the VES points down to about 40 m. However, it was observed that the axial length had overriding sandy matter with high porosity and potentially rife for great infiltration; a condition that could facilitate seepage around the reservoir portion of the dam.